This application relates to measuring current through an electrical conductor.
Coils such as Rogowski coils are used to measure current through an electrical conductor.
In one general aspect, a coil includes a first portion, a second portion, a third portion, and a fourth portion. The first portion is wound in a first direction around a first core and the second portion is wound in the first direction around a second core. The third portion is wound in a second direction that is different from the first direction around a third core such that the third portion is decoupled from the first and second portions. Additionally, the fourth portion is wound in the second direction around a fourth core and decoupled from the first and second portions. A inner area is formed by arranging the portions such that the first portion mates with the second portion and the third portion mates with the fourth portion. A voltage is induced in the coil if an electrical conductor is placed in the inner area.
Implementations may include one or more of the following features. For example the first and third portions may be connected at a first connection point, the third and fourth portions may be connected at a second connection point, and the fourth and second portions may be connected at a third connection point. In this case, the voltage induced in the coil may be measured across the first and second portions of the coil. Alternatively, the first and second portions may be connected at a fourth connection point and the voltage induced in the coil may be measured across the second connection point and the fourth connection point.
The first portion may be traced on a first printed circuit board that forms the first core and the second portion may be traced on a second printed circuit board that forms the second core. Likewise, the third portion may be traced on a third printed circuit board that forms the third core and the fourth portion may be traced on a fourth printed circuit board that forms the fourth core. The first and second printed circuit boards may be laminated with the third and fourth printed circuit boards.
The first and second portions may mate to form a first loop and the third and fourth portions mate to form a second loop. Thus, the first and second loops may define the inner area. The first and second loops may be rectangular, circular, or elliptical.
The first direction may be clockwise and the second direction may be counterclockwise. The first, second, third, and fourth cores may be non-magnetic.
The coil may include a fifth portion wound in the first direction around a fifth core and a sixth portion wound in the second direction around a sixth core. In this case, the inner area is formed by arranging the portions such that the first, second, and fifth portions mate with each other and the third, fourth, and sixth portions mate with each other. The first, second, and fifth portions may mate to form a first loop and the third, fourth, and sixth portions mate to form a second loop.
The coil may be implemented in a system that includes a voltage measuring device that measures a voltage induced in the coil when an electrical conductor is placed in the inner area. The system may also include a current calculating device connected to the voltage measuring device and configured to calculate the current through the electrical conductor based on the measured voltage.
Aspects of the techniques and systems can include one or more of the following advantages. The coil exhibits improved current measurement accuracy because each of the portions are identically and separately wound and then located near each other. Thus, the coil can better account for effects of fields not produced by the electrical conductor. Additionally, the improved current measurement accuracy results from the reduction of unwanted influence due to external electromagnetic fields and due to internal electromagnetic fields. In particular, influence due to external fields was measured in tests to be less than or equal to 0.2% and influence due to internal fields was measured in tests to be less than or equal to 0.6%. Moreover, the accuracy of the coil matches or exceeds the accuracy of a high-precision laboratory current transformer, which is used for measuring current through an electrical conductor.
The coil may be made of any shape and size because it is made of portions that may be joined together to accommodate any size electrical conductor. Each of the first and second loops of the coil may be made of any suitable number of portions, such as, for example, three or four portions. Additionally, the shape of the coil may be adjusted by adjusting the shape of each of the portions that make up the first and second loops. One of the portions that forms a loop may have a shape that is different from the shape of the other portion that forms that loop. In this way, an asymmetrical coil may be formed.
Other features and advantages will be apparent from the description, the drawings, and the claims.